Question

I have a program that I am trying to understand but there is an abbreviated code or codes that i don’t understand.
the code is

    double xDistance = x1 - x2 >= 0 ? x1 - x2 : x2 - x1;
    double yDistance = y1 - y2 >= 0 ? y1 - y2 : y2 - y1;

i read in programming books that ?: is an abbreviated form of if…then but where do i put these words in because everytime i insert or replace some code I get a syntax error.

Also are there more than one way to write the following line of code

(xDistance <= (w1 + w2) / 2 && yDistance <= (h1 + h2) / 2)

preferably replacing the && operator

thanks in advance for any assistance given.

Answer 1

The conditional operator ? : is shorthand for if-else and works as so:

(condition) ? (return this if condition true) : (return this if condition false)

Therefore

double xDistance = x1 - x2 >= 0 ? x1 - x2 : x2 - x1;

equates to:

if (x1 - x2 >= 0)
   xDistance = x1 - x2;
else
   xDistance = x2 - x1;

The second line:

double yDistance = y1 - y2 >= 0 ? y1 - y2 : y2 - y1;

is the same thing, equates to:

if (y1 - y2 >= 0)
   yDistance = y1 - y2;
else
   yDistance = y2 - y1;

Which is storing the absolute values (ie. distance rather than displacement) in xDistance and yDistance. Can also be replaced with Math.abs(x1 - x2), etc.

And why do you want to replace the && operator in the following?

(xDistance <= (w1 + w2) / 2 && yDistance <= (h1 + h2) / 2)

If you really had to you could have (assuming this statement belongs in an if statement):

if (xDistance <= (w1 + w2) / 2)
   if (yDistance <= (h1 + h2) / 2)
      // do something

EDIT: As mentioned by David in the comments, && is simply a logical AND. ie. for X && Y, the expression is TRUE iff both X is TRUE and Y is TRUE.

Because of this you can take advantage of short-circuiting, where if the first condition (X) is FALSE, then there is no point in the program evaluating the second (Y) since the expression can never be TRUE.